TUN-8688: Correct UDP bind for IPv6 edge connectivity on macOS

For macOS, we want to set the DF bit for the UDP packets used by the QUIC
connection; to achieve this, you need to explicitly set the network
to either "udp4" or "udp6". When determining which network type to pick
we need to use the edge IP address chosen to align with what the local
IP family interface we will use. This means we want cloudflared to bind
to local interfaces for a random port, so we provide a zero IP and 0 port
number (ex. 0.0.0.0:0). However, instead of providing the zero IP, we
can leave the value as nil and let the kernel decide which interface and
pick a random port as defined by the target edge IP family.

This was previously broken for IPv6-only edge connectivity on macOS and
all other operating systems should be unaffected because the network type
was left as default "udp" which will rely on the provided local or remote
IP for selection.

Closes TUN-8688

connection/quic.go

@@ -90,7 +90,7 @@ type QUICConnection struct {
 func NewQUICConnection(
 	ctx context.Context,
 	quicConfig *quic.Config,
-	edgeAddr net.Addr,
+	edgeAddr netip.AddrPort,
 	localAddr net.IP,
 	connIndex uint8,
 	tlsConfig *tls.Config,
@@ -103,12 +103,12 @@ func NewQUICConnection(
 	streamWriteTimeout time.Duration,
 	gracePeriod time.Duration,
 ) (*QUICConnection, error) {
-	udpConn, err := createUDPConnForConnIndex(connIndex, localAddr, logger)
+	udpConn, err := createUDPConnForConnIndex(connIndex, localAddr, edgeAddr, logger)
 	if err != nil {
 		return nil, err
 	}
 
-	session, err := quic.Dial(ctx, udpConn, edgeAddr, tlsConfig, quicConfig)
+	session, err := quic.Dial(ctx, udpConn, net.UDPAddrFromAddrPort(edgeAddr), tlsConfig, quicConfig)
 	if err != nil {
 		// close the udp server socket in case of error connecting to the edge
 		udpConn.Close()
@@ -641,18 +641,15 @@ func (rp *muxerWrapper) Close() error {
 	return nil
 }
 
-func createUDPConnForConnIndex(connIndex uint8, localIP net.IP, logger *zerolog.Logger) (*net.UDPConn, error) {
+func createUDPConnForConnIndex(connIndex uint8, localIP net.IP, edgeIP netip.AddrPort, logger *zerolog.Logger) (*net.UDPConn, error) {
 	portMapMutex.Lock()
 	defer portMapMutex.Unlock()
 
-	if localIP == nil {
-		localIP = net.IPv4zero
-	}
-
 	listenNetwork := "udp"
-	// https://github.com/quic-go/quic-go/issues/3793 DF bit cannot be set for dual stack listener on OSX
+	// https://github.com/quic-go/quic-go/issues/3793 DF bit cannot be set for dual stack listener ("udp") on macOS,
+	// to set the DF bit properly, the network string needs to be specific to the IP family.
 	if runtime.GOOS == "darwin" {
-		if localIP.To4() != nil {
+		if edgeIP.Addr().Is4() {
 			listenNetwork = "udp4"
 		} else {
 			listenNetwork = "udp6"

connection/quic_test.go

@@ -13,6 +13,7 @@ import (
 	"math/big"
 	"net"
 	"net/http"
+	"net/netip"
 	"net/url"
 	"os"
 	"strings"
@@ -26,6 +27,7 @@ import (
 	"github.com/rs/zerolog"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"golang.org/x/net/nettest"
 
 	"github.com/cloudflare/cloudflared/datagramsession"
 	cfdquic "github.com/cloudflare/cloudflared/quic"
@@ -162,7 +164,7 @@ func TestQUICServer(t *testing.T) {
 				close(serverDone)
 			}()
 
-			qc := testQUICConnection(udpListener.LocalAddr(), t, uint8(i))
+			qc := testQUICConnection(netip.MustParseAddrPort(udpListener.LocalAddr().String()), t, uint8(i))
 
 			connDone := make(chan struct{})
 			go func() {
@@ -632,7 +634,6 @@ func TestServeUDPSession(t *testing.T) {
 	defer udpListener.Close()
 
 	ctx, cancel := context.WithCancel(context.Background())
-	val := udpListener.LocalAddr()
 
 	// Establish QUIC connection with edge
 	edgeQUICSessionChan := make(chan quic.Connection)
@@ -646,7 +647,7 @@ func TestServeUDPSession(t *testing.T) {
 	}()
 
 	// Random index to avoid reusing port
-	qc := testQUICConnection(val, t, 28)
+	qc := testQUICConnection(netip.MustParseAddrPort(udpListener.LocalAddr().String()), t, 28)
 	go qc.Serve(ctx)
 
 	edgeQUICSession := <-edgeQUICSessionChan
@@ -695,8 +696,20 @@ func TestNopCloserReadWriterCloseAfterEOF(t *testing.T) {
 }
 
 func TestCreateUDPConnReuseSourcePort(t *testing.T) {
+	edgeIPv4 := netip.MustParseAddrPort("0.0.0.0:0")
+	edgeIPv6 := netip.MustParseAddrPort("[::]:0")
+
+	// We assume the test environment has access to an IPv4 interface
+	testCreateUDPConnReuseSourcePortForEdgeIP(t, edgeIPv4)
+
+	if nettest.SupportsIPv6() {
+		testCreateUDPConnReuseSourcePortForEdgeIP(t, edgeIPv6)
+	}
+}
+
+func testCreateUDPConnReuseSourcePortForEdgeIP(t *testing.T, edgeIP netip.AddrPort) {
 	logger := zerolog.Nop()
-	conn, err := createUDPConnForConnIndex(0, nil, &logger)
+	conn, err := createUDPConnForConnIndex(0, nil, edgeIP, &logger)
 	require.NoError(t, err)
 
 	getPortFunc := func(conn *net.UDPConn) int {
@@ -710,17 +723,17 @@ func TestCreateUDPConnReuseSourcePort(t *testing.T) {
 	conn.Close()
 
 	// should get the same port as before.
-	conn, err = createUDPConnForConnIndex(0, nil, &logger)
+	conn, err = createUDPConnForConnIndex(0, nil, edgeIP, &logger)
 	require.NoError(t, err)
 	require.Equal(t, initialPort, getPortFunc(conn))
 
 	// new index, should get a different port
-	conn1, err := createUDPConnForConnIndex(1, nil, &logger)
+	conn1, err := createUDPConnForConnIndex(1, nil, edgeIP, &logger)
 	require.NoError(t, err)
 	require.NotEqual(t, initialPort, getPortFunc(conn1))
 
 	// not closing the conn and trying to obtain a new conn for same index should give a different random port
-	conn, err = createUDPConnForConnIndex(0, nil, &logger)
+	conn, err = createUDPConnForConnIndex(0, nil, edgeIP, &logger)
 	require.NoError(t, err)
 	require.NotEqual(t, initialPort, getPortFunc(conn))
 }
@@ -832,7 +845,7 @@ func (s mockSessionRPCServer) UnregisterUdpSession(ctx context.Context, sessionI
 	return nil
 }
 
-func testQUICConnection(udpListenerAddr net.Addr, t *testing.T, index uint8) *QUICConnection {
+func testQUICConnection(udpListenerAddr netip.AddrPort, t *testing.T, index uint8) *QUICConnection {
 	tlsClientConfig := &tls.Config{
 		InsecureSkipVerify: true,
 		NextProtos:         []string{"argotunnel"},